The class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon has been known for some time. Nozaki, e.g., U.S. Pat. No. 3,694,412, produced such polymers in the presence of arylphosphine complexes of palladium moieties as catalyst and certain inert solvents. More recent procedures for the production of the linear alternating polymers, now known as polyketones or polyketone polymers, are illustrated by a number of published European Patent Applications including Nos. 121,965, 181,014, 213,671 and 257,663. These processes involve the use of a catalyst composition formed from a compound of palladium, nickel or cobalt, the anion of a strong non-hydrohalogenic acid and a bidentate ligand of phosphorus, arsenic, antimony or nitrogen. The resulting polymers are relatively high molecular weight materials having established utility as premium thermoplastics.
The polymerization to produce the linear alternating polymers is conducted by a variety of process methods. In a batch process, the reactants, catalyst composition and a reaction diluent are charged to a suitable reactor operating under polymerization conditions. In a batch process, only the reaction temperature stays constant and other reaction variables change over time. In a semi-continuous process, the reaction pressure is held constant by continued addition of monomeric reactants as polymerization proceeds. From a number of considerations a continuous process of polymerization affords even greater advantages. The monomeric reactants, catalyst composition and reaction diluent are continuously provided to the reactor. The polymer product, as a suspension in the reaction diluent, increases in concentration until a steady state is reached. At this point, product suspension of substantially constant concentration is withdrawn from the reactor. The polymer so produced will have substantially constant properties.
At steady state polymerization, the actual polymer suspension concentration is important as is the bulk density of the polymer. The higher the polymer suspension concentration, up to the point where the viscosity of the mixture renders further heat removal difficult, the greater the amount of polymer that can be made per unit of reaction diluent. The greater the bulk density of the polymer the larger the amount of polymer that can be made in a reactor of given volume.
The polymer suspension concentration and bulk density at steady state polymerization have been found to depend to a considerable extent upon the manner in which the polymerization has been initiated or "started-up". The start-up period is that part of the polymerization time which takes place before the steady state polymerization is reached. In copending U.S. patent application Ser. No. 668,848, filed Mar. 13, 1991 there is described a start-up procedure which results in desirable polymer suspension concentrations and polymer bulk densities under steady state operation. In this procedure, the concentration of the catalyst composition is initially lower than that required for steady state operation but increases during the initiation or start-up period. Despite the desirable results of this start-up procedure, it is on occasion somewhat slow. It would be of advantage to provide an improved start-up procedure for initiating the polymerization of carbon monoxide and at least one ethylenically unsaturated hydrocarbon to produce linear alternating polymers.